The invention relates generally to infusion systems, and more particularly, to an apparatus and method for controlling the volume flow rate of infusion fluid through an infusion pump.
A typical infusion system for use in the medical field includes an infusion fluid container that supplies infusion fluid to a drip chamber. The drip chamber is typically made of a transparent resin. The drip chamber, in turn, supplies the fluid to an infusion tube which passes through an infusion pump. As disclosed in Japanese patent publication No. Hei-4-51963, an apparatus and method for controlling infusion volume typically involves setting the rate at which fluid flows through the infusion pump to match the rate at which fluid flows into the drip chamber. A photo coupler flow sensor is used to detect drops of fluid entering the drip chamber. The number of drops of fluid dripping into the drip chamber is counted over a specified period of time by a computer, typically contained in the infusion pump. The volume flow rate of fluid into the drip chamber is then calculated by the computer. Using this calculated volume flow rate, the infusion-pump motor is adjusted so that the desired volume flow rate of fluid through the infusion pump matches the measured flow rate into the drip chamber.
Under a steady-state environment, i.e., one in which the drip chamber remains motionless, the method and apparatus of controlling volume flow rate as just described provides smooth and continuous infusion. However, in some environments in which infusion systems operate, it is generally impracticable to expect a drip-chamber to remain motionless. A sway or vibration of the drip chamber may occur at a bedside or in a clinical environment due to the movement of a patient. Uncontrollable environmental conditions, such as wind, may also cause the drip chamber to move.
When the drip chamber experiences such movement, existing sensors may not successfully accommodate for the effect such movement has on the operation of the drip chamber. This is because the accuracy of the flow rate is largely dependent on the accuracy of the drip-chamber drop count. If the drip chamber is caused to sway or vibrate, the flow sensor may not detect all the drops and accordingly the count is inaccurate. If movement occurs and the drip-chamber drop count is inaccurate, the infusion volume flow rate of the infusion pump does not accurately reflect the flow rate in the drip chamber. When such movement occurs, existing apparatus have the disadvantageous feature of stopping the infusion pump and ceasing infusion.
Hence, those skilled in the art have recognized a need for an apparatus and a method to ensure continuous and accurate infusion even where uncontrollable environmental conditions cause the infusion system, specifically the drip chamber, to move. The invention fulfills these needs and other.